With the development of Internet of Things (IoT), which involves internetworking of physical devices, it is important for a physical device to have a long lifetime. As most IoT devices rely on battery, the demand for batteries increases significantly and thus raises environmental issues. A technique called energy harvesting has been developed to reduce the demand for batteries in IoT devices. Energy harvesters, such as photovoltaic cells, thermoelectric generators, and piezoelectric generators, have been widely used and researched. In particular, photovoltaic cells are used in indoor light energy harvesting applications and thermoelectric generators are used in room temperature energy harvesting applications. In order to effectively charge the system powered by the energy harvester, a maximum power point tracking (MPPT) technique may be adopted to control the energy harvester to supply the maximum power, hence enhancing energy harvesting efficiency and reducing the charging time.